FIG. 1 depicts an automobile or other motor vehicle 100 equipped with a hands-free cellular telephone 102, which provides two-way voice and data communication via a cellular telephone network 104. The cellular telephone 102 and the network 104 that the cell phone 102 communicates through, provide occupants of the vehicle with the ability to carry on a two-way voice conversation via a cellular telephone 105 located away from the vehicle 100.
While cellular networks are nearly ubiquitous and the communications they provide quite reliable, the audio of a “hands-free” cellular telephone continues to suffer from a phenomena known as far-end echo. In FIG. 1, voice or other audio signals 106 output from a loud speaker 108 are at an amplitude that is great enough to allow the audio signals 106 to be heard by a driver 110 or other vehicle occupants. Those audio signals are thus inherently strong enough to be sensed or “picked up” by a hands-free microphone 112 within the vehicle 100.
During a hands-free call between the cellular telephone 102 in the vehicle and the remote or “far end” cell phone 105, audio signals detected by the hands-free microphone 112 are transmitted from the cellular telephone 102 to the distant or “far end” cell phone 105. Since the audio output from the speaker 108 needs to be loud enough for the driver 110 and vehicle occupants to hear, the audio from the speaker 108 will also be picked-up by the microphone 112. Audio that is output from the speaker 108 that originates from the far end cell phone 105 will thus be picked up by the microphone 112 and sent back to the far end cell phone 105 as an “echo.”
Far end audio echo, i.e., audio from a far end that is picked up at the “near end” and re-transmitted back to the far end, can be reduced by filtering the output of a hands-free phone microphone 112 at the near end of a connection, however prior art echo suppressors are unable to completely suppress far end echo. A method and apparatus for suppressing echo that remains in a signal after being LMS filtered would be an improvement.